Simplified Extension Example

db/assoc_extension.cds_

@@ -1,65 +1,44 @@
-using {sap.capire.bookshop} from '_base/db/schema';
+using {sap.capire.bookshop} from '_base/db/schema';
-using {sap.capire.orders}   from '_base/db/schema';
+using {sap.capire.orders}   from '_base/db/schema';
-using from '_base/db/capire_common';
+using from '_base/db/capire_common';
-
+//using {Z_bookshop.fieldExtension as field} from './field_extension';
-using {
+
-    cuid, managed, Country, sap.common.CodeList
+using {
-} from '@sap/cds/common';
+    cuid, managed, Country, sap.common.CodeList
-
+} from '@sap/cds/common';
-
+
-
+
-namespace Z_bookshop.extension;
+
-
+namespace Z_bookshop.assocExtension;
-
+
-// extend existing entity 
+
-extend orders.Orders with { 
+// extend existing entity 
-  Z_Customer    : Association to one Z_Customers;  
+extend orders.Orders with { 
-  Z_SalesRegion : Association to one Z_SalesRegion; 
+  Z_Customer    : Association to one Z_Customers;  
-  Z_priority    : String @assert.range enum {high; medium; low} default 'medium';
+  Z_SalesRegion : Association to one Z_SalesRegion; 
-  Z_Remarks     : Composition of many Z_Remarks on Z_Remarks.parent = $self;
+}
-}  
+
-
+// new entity - as association target
-
+entity Z_Customers : cuid, managed 
-// new entity - as association target
+{
-entity Z_Customers : cuid, managed 
+  email        : String;
-{
+  firstName    : String;
-  email        : String;
+  lastName     : String; 
-  firstName    : String;
+  creditCardNo : String;
-  lastName     : String; 
+  dateOfBirth  : Date;
-  creditCardNo : String;
+  status       : String   @assert.range enum {platinum; gold; silver; bronze} default 'bronze';
-  dateOfBirth  : Date;
+  creditScore  : Decimal  @assert.range: [ 1.0, 100.0 ] default 50.0;
-  status       : String   @assert.range enum {platinum; gold; silver; bronze} default 'bronze';
+  
-  creditScore  : Decimal  @assert.range: [ 1.0, 100.0 ] default 50.0;
+}
-  PostalAddresses : Composition of many Z_CustomerPostalAddresses on PostalAddresses.Customer = $self;
+
-}
+// new unique constraint (secondary index)
-
+annotate Z_Customers with @assert.unique: { email: [ email ] }   
-// new unique constraint (secondary index)
+{
-annotate Z_Customers with @assert.unique: { email: [ email ] }   
+  email @mandatory;    // mandatory check
-{
+}
-  email @mandatory;    // mandatory check
+
-}
+
-
+// new entity - as code list
-// new entity - as composition target
+entity Z_SalesRegion: CodeList {
-entity Z_CustomerPostalAddresses : cuid, managed 
+  key regionCode : String(11);
-{
+}
-  Customer       : Association to one Z_Customers;
-  description    : String;
-  street         : String;
-  town           : String;
-  country        : Country;
-}
-
-// new entity - as code list
-entity Z_SalesRegion: CodeList {
-  key regionCode : String(11);
-}
-
-
-// new entity - as composition target
-entity Z_Remarks : cuid, managed
-{  
-  parent      : Association to one orders.Orders;  
-  number      : Integer;  
-  remarksLine : String; 
-}
-

db/comp_extension.cds_

@@ -0,0 +1,41 @@
+using {sap.capire.bookshop} from '_base/db/schema';
+using {sap.capire.orders}   from '_base/db/schema';
+using from '_base/db/capire_common';
+using {Z_bookshop.assocExtension as assoc} from './assoc_extension';
+
+using {
+    cuid, managed, Country, sap.common.CodeList
+} from '@sap/cds/common';
+
+
+
+namespace Z_bookshop.compExtension;
+
+
+// extend existing entity 
+extend orders.Orders with { 
+  Z_Remarks     : Composition of many Z_Remarks on Z_Remarks.parent = $self;
+}  
+
+// new entity - as composition target
+entity Z_CustomerPostalAddresses : cuid, managed 
+{
+  Customer       : Association to one assoc.Z_Customers;
+  description    : String;
+  street         : String;
+  town           : String;
+  country        : Country;
+}
+
+
+// new entity - as composition target
+entity Z_Remarks : cuid, managed
+{  
+  parent      : Association to one orders.Orders;  
+  number      : Integer;  
+  remarksLine : String; 
+}
+
+extend assoc.Z_Customers with {
+  PostalAddresses : Composition of many Z_CustomerPostalAddresses on PostalAddresses.Customer = $self;
+}

db/data/Z_bookshop.extension-Z_CustomerPostalAddresses.csv_

@@ -1,5 +1,5 @@
-ID;modifiedAt;createdAt;createdBy;modifiedBy;Customer_ID;description;street;town;country_code
+ID;modifiedAt;createdAt;createdBy;modifiedBy;Customer_ID;description;street;town;country_code
-1e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-04-04;2019-01-31;admin@business.com;admin@business.com;8e2f2640-6866-4dcf-8f4d-3027aa831cad;Home;Hauptstrasse 11;Berlin;DE
+1e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-04-04;2019-01-31;admin@business.com;admin@business.com;8e2f2640-6866-4dcf-8f4d-3027aa831cad;Home;Hauptstrasse 11;Berlin;DE
-24e718c9-ff99-47f1-8ca3-950c850777d4;2019-04-04;2019-01-30;admin@business.com;admin@business.com;74e718c9-ff99-47f1-8ca3-950c850777d4;Home;Main Street 22;London;GB
+24e718c9-ff99-47f1-8ca3-950c850777d4;2019-04-04;2019-01-30;admin@business.com;admin@business.com;74e718c9-ff99-47f1-8ca3-950c850777d4;Home;Main Street 22;London;GB
-3e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-04-04;2019-01-31;admin@business.com;admin@business.com;8e2f2640-6866-4dcf-8f4d-3027aa831cad;Work;Siemensstrasse 21;Berlin;DE
+3e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-04-04;2019-01-31;admin@business.com;admin@business.com;8e2f2640-6866-4dcf-8f4d-3027aa831cad;Work;Siemensstrasse 21;Berlin;DE
-44e718c9-ff99-47f1-8ca3-950c850777d4;2019-04-04;2019-01-30;admin@business.com;admin@business.com;74e718c9-ff99-47f1-8ca3-950c850777d4;Work;Work Street 34;London;GB
+44e718c9-ff99-47f1-8ca3-950c850777d4;2019-04-04;2019-01-30;admin@business.com;admin@business.com;74e718c9-ff99-47f1-8ca3-950c850777d4;Work;Work Street 34;London;GB

db/data/Z_bookshop.extension-Z_Customers.csv_

@@ -1,3 +1,3 @@
-ID;modifiedAt;createdAt;createdBy;modifiedBy;email;firstName;lastName;creditCardNo;dateOfBirth;status;creditScore
+ID;modifiedAt;createdAt;createdBy;modifiedBy;email;firstName;lastName;creditCardNo;dateOfBirth;status;creditScore
-8e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-04-04;2019-01-31;admin@business.com;admin@business.com;john.doe@test.com;John;Doe;9977-6655-4433-2211;1970-01-01;gold;80.0
+8e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-04-04;2019-01-31;admin@business.com;admin@business.com;john.doe@test.com;John;Doe;9977-6655-4433-2211;1970-01-01;gold;80.0
 74e718c9-ff99-47f1-8ca3-950c850777d4;2019-04-04;2019-01-30;admin@business.com;admin@business.com;jane.doe@sap.com;Jane;Doe;2211-3344-5566-7788;1980-11-11;platinum;100.0

db/data/Z_bookshop.extension-Z_SalesRegion.csv_

@@ -1,4 +1,4 @@
-regionCode;name;descr
+regionCode;name;descr
-AMER;Americas;North, Central and South America
+AMER;Americas;North, Central and South America
-EMEA;Europe, the Middle East and Africa;Europe, the Middle East and Africa
+EMEA;Europe, the Middle East and Africa;Europe, the Middle East and Africa
 APJ;Asia Pacific and Japan;Asia Pacific and Japan

db/data/sap.capire.orders-Orders.csv

@@ -1,3 +1,3 @@
-ID;createdAt;createdBy;buyer;OrderNo;currency_code;Z_Customer_ID;Z_priority;Z_SalesRegion_regionCode
+ID;createdAt;createdBy;buyer;OrderNo;currency_code;Z_orderInfo;Z_internalNo;Z_expectedDelivery;Z_priority;Z_discount;
-7e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-01-31;john.doe@test.com;john.doe@test.com;1;EUR;8e2f2640-6866-4dcf-8f4d-3027aa831cad;high;EMEA
+7e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-01-31;john.doe@test.com;john.doe@test.com;1;EUR;Webshop order;202001;2019-03-31;high;5.0
-64e718c9-ff99-47f1-8ca3-950c850777d4;2019-01-30;jane.doe@test.com;jane.doe@test.com;2;EUR;74e718c9-ff99-47f1-8ca3-950c850777d4;low;APJ
+64e718c9-ff99-47f1-8ca3-950c850777d4;2019-01-30;jane.doe@test.com;jane.doe@test.com;2;EUR;Walk in order;202002;2019-04-15;low;10.0

db/data/sap.capire.orders-Orders.csv_

@@ -0,0 +1,3 @@
+ID;createdAt;createdBy;buyer;OrderNo;currency_code;Z_Customer_ID;Z_priority;Z_SalesRegion_regionCode
+7e2f2640-6866-4dcf-8f4d-3027aa831cad;2019-01-31;john.doe@test.com;john.doe@test.com;1;EUR;8e2f2640-6866-4dcf-8f4d-3027aa831cad;high;EMEA
+64e718c9-ff99-47f1-8ca3-950c850777d4;2019-01-30;jane.doe@test.com;jane.doe@test.com;2;EUR;74e718c9-ff99-47f1-8ca3-950c850777d4;low;APJ

db/field_extension.cds

@@ -0,0 +1,38 @@
+using {sap.capire.bookshop} from '_base/db/schema';
+using {sap.capire.orders} from '_base/db/schema';
+using from '_base/db/capire_common';
+
+using {
+  cuid,
+  managed,
+  Country,
+  sap.common.CodeList
+} from '@sap/cds/common';
+
+
+namespace Z_bookshop.fieldExtension;
+
+
+// extend existing entity
+extend orders.Orders with {
+  Z_orderInfo        : String default 'Webshop order';
+  Z_internalNo       : Integer; // uniqiue constraint
+  Z_expectedDelivery : Date; //mandatory
+  Z_priority         : String
+      @assert.range enum {
+      high;
+      medium;
+      low
+    } default 'medium';
+    Z_discount       : Decimal
+      @assert.range : [
+        0.0,
+        99.9
+      ] default 0.0;
+    }
+
+
+// new unique constraint (secondary index)
+annotate orders.Orders with @assert.unique : {Z_internalNo : [Z_internalNo]} {
+  Z_expectedDelivery @mandatory; // mandatory check
+}

srv/extension_service.cds

@@ -2,11 +2,5 @@ using from '_base/srv/admin-service';
 using from '_base/srv/cat-service';
 using from '_base/srv/orders-service';
 
-using { Z_bookshop.extension as ext } from '../db/extension';
+using from '../db/field_extension';
-
-
-extend service OrdersService with {
-   entity Z_Customers   as projection on ext.Z_Customers;
-   entity Z_SalesRegion as projection on ext.Z_SalesRegion;
-}
 

srv/extension_service_compassoc.cds_

@@ -0,0 +1,14 @@
+using from '_base/srv/admin-service';
+using from '_base/srv/cat-service';
+using from '_base/srv/orders-service';
+
+using from '../db/field_extension';
+using { Z_bookshop.compExtension as comp } from '../db/comp_extension';
+using { Z_bookshop.assocExtension as assoc } from '../db/assoc_extension';
+
+
+extend service OrdersService with {
+   entity Z_Customers   as projection on assoc.Z_Customers;
+   entity Z_SalesRegion as projection on assoc.Z_SalesRegion;
+}
+

srv/extension_service_ui.cds

@@ -1,260 +0,0 @@
-using from '_base/app/services';
-using OrdersService from './extension_service';
-
-
-// new entity -- draft enabled
-annotate OrdersService.Z_Customers   with @odata.draft.enabled;
-// new codelist entity -- draft enabled
-annotate OrdersService.Z_SalesRegion with @odata.draft.enabled;
-
-
-// new entity -- titles
-annotate OrdersService.Z_Customers with {
-    ID           @(     
-        UI.Hidden,
-        Common : {Text : email}
-    );
-    firstName    @title : 'First Name';
-    lastName     @title : 'Last Name';
-    email        @title : 'Email';
-    creditCardNo @title : 'Credit Card No';
-    dateOfBirth  @title : 'Date of Birth';
-	status       @title : 'Status';
-	creditScore  @title : 'Credit Score';
-}
-
-// new entity -- titles
-annotate OrdersService.Z_CustomerPostalAddresses with {
-    ID          @(       
-        UI.Hidden,
-        Common : {Text : description}
-    );
-    description @title : 'Description';
-    street      @title : 'Street';
-    town        @title : 'Town';
-    country     @title : 'Country';
-}
-
-// new entity -- titles
-annotate OrdersService.Z_SalesRegion with {
-	regionCode      @title: 'Region Code';
-}
-
-// new entity -- titles
-annotate OrdersService.Z_Remarks with {
-    number          @title: 'Remark Number';
-	remarksLine     @title: 'Remark';
-}
-
-
-// new entity in service -- UI
-annotate OrdersService.Z_Customers with @(UI : {
-    HeaderInfo       : {
-        TypeName       : 'Customer',
-        TypeNamePlural : 'Customers',
-        Title          : {
-            $Type : 'UI.DataField',
-            Value : email
-        }
-    },
-    LineItem         : [
-        {Value : firstName},
-        {Value : lastName},
-        {Value : email},
-		{Value : status},
-        {Value : creditScore}
-    ],
-    Facets           : [
-		{$Type: 'UI.ReferenceFacet', Label: 'Main', Target : '@UI.FieldGroup#Main'},
-		{$Type: 'UI.ReferenceFacet', Label: 'Customer Postal Addresses', Target: 'PostalAddresses/@UI.LineItem'}
-	],
-    FieldGroup #Main : {Data : [
-        {Value : firstName},
-        {Value : lastName},
-        {Value : email},
-		{Value : status},
-        {Value : creditScore}
-    ]}
-} ) ;
-
-// new entity -- UI
-annotate OrdersService.Z_CustomerPostalAddresses with @(UI : {
-    HeaderInfo       : {
-        TypeName       : 'CustomerPostalAddress',
-        TypeNamePlural : 'CustomerPostalAddresses',
-        Title          : {
-            $Type : 'UI.DataField',
-            Value : description
-        }
-    },
-    LineItem         : [
-        {Value : description},
-        {Value : street},
-        {Value : town},
-		{Value : country_code}
-	],
-    Facets           : [
-		{$Type: 'UI.ReferenceFacet', Label: 'Main', Target : '@UI.FieldGroup#Main'}
-	],
-    FieldGroup #Main : {Data : [
-        {Value : description},
-        {Value : street},
-        {Value : town},
-		{Value : country_code}
-    ]}
-}, ) {
-
-};
-
-// new entity -- UI
-annotate OrdersService.Z_SalesRegion with @(
-	UI: {
-		HeaderInfo: {
-			TypeName: 'Sales Region',
-			TypeNamePlural: 'Sales Regions',
-			Title          : {
-                $Type : 'UI.DataField',
-                Value : regionCode
-            }
-		},
-		LineItem: [
-			{Value: regionCode},   
-            {Value: name}, 
-            {Value: descr}   
-		],
-		Facets: [
-			{$Type: 'UI.ReferenceFacet', Label: 'Main',    Target: '@UI.FieldGroup#Main'}
-		],
-		FieldGroup#Main: {
-			Data: [
-		        {Value: regionCode},   
-				{Value: name}, 
-                {Value: descr}     
-			]
-		}
-	},
-) {
-
-};
-
-
-// new entity -- UI
-annotate OrdersService.Z_Remarks with @(
-	UI: {
-		HeaderInfo: {
-			TypeName: 'Remark',
-			TypeNamePlural: 'Remarks',
-			Title          : {
-                $Type : 'UI.DataField',
-				Value : number
-            }
-		},
-		LineItem: [
-			{Value: number},
-			{Value: remarksLine}       
-		],
-		Facets: [
-			{$Type: 'UI.ReferenceFacet', Label: 'Main',    Target: '@UI.FieldGroup#Main'}
-		],
-		FieldGroup#Main: {
-			Data: [
-		        {Value: number},
-			    {Value: remarksLine}       
-			]
-		}
-	},
-) {
-
-};
-
-// extend existing entity Orders with new extension fields and new composition
-
-@odata.draft.enabled
-annotate OrdersService.Orders with @(
-	UI: {
-		SelectionFields: [ createdAt, createdBy ],
-		LineItem: [
-			{Value: OrderNo, Label:'OrderNo'},
-			{Value: Z_Customer_ID, Label:'Customer'},                 // extension field
-			{Value: Z_SalesRegion_regionCode, Label:'Sales Region'},  // extension field
-			{Value: Z_priority,    Label:'Priority'},                 // extension field
-			{Value: createdAt,   Label:'Date'}
-		],
-		HeaderInfo: {
-			TypeName: 'Order', TypeNamePlural: 'Orders',
-			Title: {
-				Label: 'Order number ', //A label is possible but it is not considered on the ObjectPage yet
-				Value: OrderNo
-			},
-			Description: {Value: createdBy}
-		},
-		Identification: [ //Is the main field group
-			{Value: createdBy, Label:'Customer'},
-			{Value: createdAt, Label:'Date'},
-			{Value: OrderNo },
-		],
-		HeaderFacets: [
-			{$Type: 'UI.ReferenceFacet', Label: '{i18n>Created}',  Target: '@UI.FieldGroup#Created'},
-			{$Type: 'UI.ReferenceFacet', Label: '{i18n>Modified}', Target: '@UI.FieldGroup#Modified'},
-		],
-		Facets: [
-			{$Type: 'UI.ReferenceFacet', Label: '{i18n>Details}',    Target: '@UI.FieldGroup#Details'},
-			{$Type: 'UI.ReferenceFacet', Label: '{i18n>OrderItems}', Target: 'Items/@UI.LineItem'},
-			{$Type: 'UI.ReferenceFacet', Label: 'Remarks',           Target: 'Z_Remarks/@UI.LineItem'} // new composition		
-		],
-		FieldGroup#Details: {
-			Data: [
-				{Value: currency_code, Label:'Currency'},                  
-				{Value: Z_Customer_ID, Label:'Customer'},                 // extension field
-				{Value: Z_SalesRegion_regionCode, Label:'Sales Region'},  // extension field
-				{Value: Z_priority,    Label:'Priority'}                  // extension field
-			]
-		},
-		FieldGroup#Created: {
-			Data: [
-				{Value: createdBy},
-				{Value: createdAt},
-			]
-		},
-		FieldGroup#Modified: {
-			Data: [
-				{Value: modifiedBy},
-				{Value: modifiedAt},
-			]
-		},
-	},
-) 
-
-{
-	createdAt @UI.HiddenFilter:false;
-	createdBy @UI.HiddenFilter:false;
-}
-;
-
-
-
-// new field in existing service -- exchange ID with text
- annotate OrdersService.Orders with {
-	Z_Customer @(
-		Common: {
-			//show email, not id for Customer in the context of Orders
-			Text: Z_Customer.email  , TextArrangement: #TextOnly,
-			ValueList: {
-				Label: 'Customers',
-				CollectionPath: 'Z_Customers',
-				Parameters: [
-					{ $Type: 'Common.ValueListParameterInOut',
-						LocalDataProperty: Z_Customer_ID,  
-						ValueListProperty: 'ID'            
-					},
-					{ $Type: 'Common.ValueListParameterDisplayOnly',
-						ValueListProperty: 'email'
-					}
-				]
-			}
-		} 
-	);
-} 
-
-
-

srv/extension_service_ui_assoc.cds_

@@ -0,0 +1,311 @@
+using from '_base/app/services';
+using OrdersService from './extension_service';
+
+
+// new entity -- draft enabled
+annotate OrdersService.Z_Customers with @odata.draft.enabled;
+// new codelist entity -- draft enabled
+annotate OrdersService.Z_SalesRegion with @odata.draft.enabled;
+
+
+// new entity -- titles
+annotate OrdersService.Z_Customers with {
+  ID           @(
+    UI.Hidden,
+    Common : {Text : email}
+  );
+  firstName    @title : 'First Name';
+  lastName     @title : 'Last Name';
+  email        @title : 'Email';
+  creditCardNo @title : 'Credit Card No';
+  dateOfBirth  @title : 'Date of Birth';
+  status       @title : 'Status';
+  creditScore  @title : 'Credit Score';
+}
+
+// new entity -- titles
+annotate OrdersService.Z_CustomerPostalAddresses with {
+  ID          @(
+    UI.Hidden,
+    Common : {Text : description}
+  );
+  description @title : 'Description';
+  street      @title : 'Street';
+  town        @title : 'Town';
+  country     @title : 'Country';
+}
+
+// new entity -- titles
+annotate OrdersService.Z_SalesRegion with {
+  regionCode @title : 'Region Code';
+}
+
+// new entity -- titles
+annotate OrdersService.Z_Remarks with {
+  number      @title : 'Remark Number';
+  remarksLine @title : 'Remark';
+}
+
+
+// new entity in service -- UI
+annotate OrdersService.Z_Customers with @(UI : {
+  HeaderInfo       : {
+    TypeName       : 'Customer',
+    TypeNamePlural : 'Customers',
+    Title          : {
+      $Type : 'UI.DataField',
+      Value : email
+    }
+  },
+  LineItem         : [
+    {Value : firstName},
+    {Value : lastName},
+    {Value : email},
+    {Value : status},
+    {Value : creditScore}
+  ],
+  Facets           : [
+    {
+      $Type  : 'UI.ReferenceFacet',
+      Label  : 'Main',
+      Target : '@UI.FieldGroup#Main'
+    },
+    {
+      $Type  : 'UI.ReferenceFacet',
+      Label  : 'Customer Postal Addresses',
+      Target : 'PostalAddresses/@UI.LineItem'
+    }
+  ],
+  FieldGroup #Main : {Data : [
+    {Value : firstName},
+    {Value : lastName},
+    {Value : email},
+    {Value : status},
+    {Value : creditScore}
+  ]}
+});
+
+// new entity -- UI
+annotate OrdersService.Z_CustomerPostalAddresses with @(UI : {
+  HeaderInfo       : {
+    TypeName       : 'CustomerPostalAddress',
+    TypeNamePlural : 'CustomerPostalAddresses',
+    Title          : {
+      $Type : 'UI.DataField',
+      Value : description
+    }
+  },
+  LineItem         : [
+    {Value : description},
+    {Value : street},
+    {Value : town},
+    {Value : country_code}
+  ],
+  Facets           : [{
+    $Type  : 'UI.ReferenceFacet',
+    Label  : 'Main',
+    Target : '@UI.FieldGroup#Main'
+  }],
+  FieldGroup #Main : {Data : [
+    {Value : description},
+    {Value : street},
+    {Value : town},
+    {Value : country_code}
+  ]}
+}, ) {
+
+};
+
+// new entity -- UI
+annotate OrdersService.Z_SalesRegion with @(UI : {
+  HeaderInfo       : {
+    TypeName       : 'Sales Region',
+    TypeNamePlural : 'Sales Regions',
+    Title          : {
+      $Type : 'UI.DataField',
+      Value : regionCode
+    }
+  },
+  LineItem         : [
+    {Value : regionCode},
+    {Value : name},
+    {Value : descr}
+  ],
+  Facets           : [{
+    $Type  : 'UI.ReferenceFacet',
+    Label  : 'Main',
+    Target : '@UI.FieldGroup#Main'
+  }],
+  FieldGroup #Main : {Data : [
+    {Value : regionCode},
+    {Value : name},
+    {Value : descr}
+  ]}
+}, ) {
+
+};
+
+
+// new entity -- UI
+annotate OrdersService.Z_Remarks with @(UI : {
+  HeaderInfo       : {
+    TypeName       : 'Remark',
+    TypeNamePlural : 'Remarks',
+    Title          : {
+      $Type : 'UI.DataField',
+      Value : number
+    }
+  },
+  LineItem         : [
+    {Value : number},
+    {Value : remarksLine}
+  ],
+  Facets           : [{
+    $Type  : 'UI.ReferenceFacet',
+    Label  : 'Main',
+    Target : '@UI.FieldGroup#Main'
+  }],
+  FieldGroup #Main : {Data : [
+    {Value : number},
+    {Value : remarksLine}
+  ]}
+}, ) {
+
+};
+
+// extend existing entity Orders with new extension fields and new composition
+
+@odata.draft.enabled
+annotate OrdersService.Orders with @(UI : {
+  SelectionFields      : [
+    createdAt,
+    createdBy
+  ],
+  LineItem             : [
+    {
+      Value : OrderNo,
+      Label : 'OrderNo'
+    },
+    {
+      Value : Z_Customer_ID,
+      Label : 'Customer'
+    }, // extension field
+    {
+      Value : Z_SalesRegion_regionCode,
+      Label : 'Sales Region'
+    }, // extension field
+    {
+      Value : Z_priority,
+      Label : 'Priority'
+    }, // extension field
+    {
+      Value : createdAt,
+      Label : 'Date'
+    }
+  ],
+  HeaderInfo           : {
+    TypeName       : 'Order',
+    TypeNamePlural : 'Orders',
+    Title          : {
+      Label : 'Order number ', //A label is possible but it is not considered on the ObjectPage yet
+      Value : OrderNo
+    },
+    Description    : {Value : createdBy}
+  },
+  Identification       : [ //Is the main field group
+    {
+      Value : createdBy,
+      Label : 'Customer'
+    },
+    {
+      Value : createdAt,
+      Label : 'Date'
+    },
+    {Value : OrderNo},
+  ],
+  HeaderFacets         : [
+    {
+      $Type  : 'UI.ReferenceFacet',
+      Label  : '{i18n>Created}',
+      Target : '@UI.FieldGroup#Created'
+    },
+    {
+      $Type  : 'UI.ReferenceFacet',
+      Label  : '{i18n>Modified}',
+      Target : '@UI.FieldGroup#Modified'
+    },
+  ],
+  Facets               : [
+    {
+      $Type  : 'UI.ReferenceFacet',
+      Label  : '{i18n>Details}',
+      Target : '@UI.FieldGroup#Details'
+    },
+    {
+      $Type  : 'UI.ReferenceFacet',
+      Label  : '{i18n>OrderItems}',
+      Target : 'Items/@UI.LineItem'
+    },
+    {
+      $Type  : 'UI.ReferenceFacet',
+      Label  : 'Remarks',
+      Target : 'Z_Remarks/@UI.LineItem'
+    } // new composition
+  ],
+  FieldGroup #Details  : {Data : [
+    {
+      Value : currency_code,
+      Label : 'Currency'
+    },
+    {
+      Value : Z_Customer_ID,
+      Label : 'Customer'
+    }, // extension field
+    {
+      Value : Z_SalesRegion_regionCode,
+      Label : 'Sales Region'
+    }, // extension field
+    {
+      Value : Z_priority,
+      Label : 'Priority'
+    } // extension field
+  ]},
+  FieldGroup #Created  : {Data : [
+    {Value : createdBy},
+    {Value : createdAt},
+  ]},
+  FieldGroup #Modified : {Data : [
+    {Value : modifiedBy},
+    {Value : modifiedAt},
+  ]},
+}, )
+
+{
+  createdAt @UI.HiddenFilter : false;
+  createdBy @UI.HiddenFilter : false;
+};
+
+
+// new field in existing service -- exchange ID with text
+annotate OrdersService.Orders with {
+  Z_Customer @(Common : {
+    //show email, not id for Customer in the context of Orders
+    Text            : Z_Customer.email,
+    TextArrangement : #TextOnly,
+    ValueList       : {
+      Label          : 'Customers',
+      CollectionPath : 'Z_Customers',
+      Parameters     : [
+        {
+          $Type             : 'Common.ValueListParameterInOut',
+          LocalDataProperty : Z_Customer_ID,
+          ValueListProperty : 'ID'
+        },
+        {
+          $Type             : 'Common.ValueListParameterDisplayOnly',
+          ValueListProperty : 'email'
+        }
+      ]
+    }
+  });
+}

srv/extension_service_ui_fields.cds

@@ -0,0 +1,70 @@
+using from '_base/app/services';
+using OrdersService from './extension_service';
+
+
+// extend existing entity Orders with new extension fields and new composition
+
+@odata.draft.enabled
+annotate OrdersService.Orders with @(UI : {
+  LineItem            : [
+    {
+      Value : OrderNo,
+      Label : 'OrderNo'
+    },
+    {
+      Value : Z_orderInfo,
+      Label : 'Additional Information'
+    }, // extension field
+    {
+      Value : Z_internalNo,
+      Label : 'Internal Order Number'
+    }, // extension field
+    {
+      Value : Z_expectedDelivery,
+      Label : 'Expecxted Delivery Date'
+    }, // extension field
+    {
+      Value : Z_priority,
+      Label : 'Priority'
+    }, // extension field
+    {
+      Value : Z_discount,
+      Label : 'Discount'
+    }, // extension field
+    {
+      Value : createdAt,
+      Label : 'Date'
+    },
+  ],
+  FieldGroup #Details : {Data : [
+    {
+      Value : currency_code,
+      Label : 'Currency'
+    },
+    {
+      Value : Z_orderInfo,
+      Label : 'Additional Information'
+    }, // extension field
+    {
+      Value : Z_internalNo,
+      Label : 'Internal Order Number'
+    }, // extension field
+    {
+      Value : Z_expectedDelivery,
+      Label : 'Expected Delivery Date'
+    }, // extension field
+    {
+      Value : Z_priority,
+      Label : 'Priority'
+    }, // extension field
+    {
+      Value : Z_discount,
+      Label : 'Discount'
+    }, // extension field
+  ]},
+})
+
+{
+  createdAt @UI.HiddenFilter : false;
+  createdBy @UI.HiddenFilter : false;
+};